Moj gležanj je natečen, ali doktor kaže da ozljeda nije ozbiljna.

Because gležanj is a masculine singular noun, and the possessive adjective moj has to agree with it in gender, number, and case.

Here the forms are:

• moj = masculine singular
• moja = feminine singular
• moje = neuter singular

So:

• moj gležanj = my ankle
• moja ozljeda = my injury

In this sentence, gležanj is in the nominative singular, so moj is too.

It is in the nominative singular.

That is because gležanj is the subject of the clause:

• Moj gležanj je natečen. = My ankle is swollen.

Croatian often uses the nominative for the subject, just as English uses the basic noun form in subject position.

Natečen is an adjective meaning swollen.

So je natečen literally means is swollen:

• je = is
• natečen = swollen

The adjective agrees with gležanj:

• gležanj is masculine singular
• so the adjective is natečen (masculine singular)

Compare:

• gležanj je natečen = masculine
• ruka je natečena = feminine
• koljeno je natečeno = neuter

Because it describes ozljeda, and ozljeda is a feminine noun.

So the adjective must match it:

• ozljeda = feminine singular
• ozbiljna = feminine singular form of serious

Compare the forms:

• ozbiljan = masculine
• ozbiljna = feminine
• ozbiljno = neuter

So:

• problem nije ozbiljan
• ozljeda nije ozbiljna
• stanje nije ozbiljno

Because in Croatian, the negative form of je is normally written as nije.

So:

• je = is
• nije = is not

This is just the standard form learners need to remember.

Examples:

• On je doktor. = He is a doctor.
• On nije doktor. = He is not a doctor.

In your sentence:

• ozljeda nije ozbiljna = the injury is not serious

After verbs like say, think, know, Croatian often introduces a full clause with da, similar to English that.

So:

• doktor kaže da ozljeda nije ozbiljna
• literally: the doctor says that the injury is not serious

In everyday English, that is often omitted, but in Croatian da is very commonly used here.

You will see this pattern a lot:

• Mislim da... = I think that...
• Znam da... = I know that...
• Kaže da... = He/she says that...

Croatian can use moj, but with body parts it is often more natural to avoid the possessive adjective and use a dative pronoun instead.

A very natural alternative is:

• Gležanj mi je natečen.

Literally this is something like The ankle to-me is swollen, but in natural English it still means My ankle is swollen.

So:

• Moj gležanj je natečen = correct, clear
• Gležanj mi je natečen = often more natural in everyday Croatian

English speakers often overuse possessives because English requires them more often.

Because Croatian has no articles like a/an/the.

That means nouns appear without an article, and definiteness is understood from context.

So:

• doktor can mean a doctor or the doctor
• ozljeda can mean an injury or the injury

In this sentence, context makes it natural to understand:

• doktor = the doctor
• ozljeda = the injury

English speakers often look for an article, but Croatian simply does not use one.

Croatian word order is more flexible than English word order.

The sentence as given is completely normal:

• Moj gležanj je natečen, ali doktor kaže da ozljeda nije ozbiljna.

But some parts could be rearranged for style, emphasis, or rhythm.

For example:

• Gležanj mi je natečen, ali doktor kaže da ozljeda nije ozbiljna.
• Doktor kaže da ozljeda nije ozbiljna, ali moj gležanj je natečen.

However, not every change sounds equally natural in every context. The original sentence is a good neutral model.

Here ali means but, and it is exactly the right word.

It connects two contrasting statements:

• My ankle is swollen
• but the injury is not serious

So:

• ali = but

It is the standard coordinating conjunction for this kind of contrast.

Yes. Both are used, but there is a slight difference in style and register.

• doktor = very common in everyday speech
• liječnik = also correct, often a bit more formal or standard

So you could say:

• Moj gležanj je natečen, ali liječnik kaže da ozljeda nije ozbiljna.

That sounds perfectly natural too.

A few sounds here are especially important for English speakers:

• ž sounds like the s in measure
• lj is a soft ly-type sound
• nj is a soft ny-type sound

So roughly:

• gležanj ≈ GLEH-zhany
• kaže ≈ KAH-zheh
• ozljeda ≈ OZ-lye-da

These are only rough English-style hints, but they help.

Also remember that Croatian spelling is very regular: words are usually pronounced much more closely to how they are written than in English.

Because Croatian, like English, uses the present tense here for both parts:

• doktor kaže = the doctor says
• ozljeda nije ozbiljna = the injury is not serious

The second part is a subordinate clause introduced by da, and it stays in the present because it describes a current situation.

So the structure is:

• main clause: doktor kaže
• subordinate clause: da ozljeda nije ozbiljna

Yes, this sentence is a good reminder that Croatian adjectives must agree with the nouns they describe.

You can see two useful patterns here:

• natečen agrees with gležanj → masculine singular
• ozbiljna agrees with ozljeda → feminine singular

So this one sentence helps reinforce a very important Croatian rule:

adjectives change form depending on the noun.

That is different from English, where swollen and serious do not change form at all.